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Sean Davison, the Kiwi scientist who was convicted for helping his mother die, plans to scan dying people's brains to test whether their stress is lowered once they know a doctor will help them die.

Davison, who heads South Africa's leading forensic DNA laboratory, has become a campaigner for legalised euthanasia after serving five months' home detention in Dunedin in 2012 for giving his dying mother a lethal dose of morphine at her request to end her pain.

Publicity about his case sparked a stream of requests from people seeking help to die, spurring him to start the lobby group Dignity South Africa in 2011.

This month, he was elected president of the World Federation of Right to Die Societies at a conference in Amsterdam also attended by former New Zealand Labour MP Maryan Street.

He is now seeking ethical approval to scan the brains of dying people to test his theory they will feel less stress if they know a doctor will help them to die quickly if their pain becomes unbearable.

"Brain scanning is complicated because they have to go into an MRI scanner," he said.

"But we have the instruments, we have the subjects available. It will take a bit longer to get the ethics approvals, and at the moment we are doing pilot projects that don't involve brain scanning."

He said brain science showed that women would benefit more if doctor-assisted death was legalised because they were less likely than men to take their own lives.

"The male doesn't have a strong link between the two hemispheres of the brain and can therefore compartmentalise thoughts and it's easier for him to end his life," he said.

"The female has a much stronger connection between the two hemispheres, which means when a woman is doing most activities you see her whole brain firing.

"For a woman, the issue becomes much more complex. A woman will take longer to make any complex decision."

He said data from Oregon showed that suicides by elderly people fell dramatically after doctor-assisted suicide was legalised in 1997.

"Forty per cent of people granted an assisted death do not take up the option," he said. "They go through the lengthy procedure of applying for it, are granted it, and don't use it. The implication is they just want the option."

Davison, 53, said he gets several requests a week from people seeking advice on the issue.

"Every night I tuck my kids into bed, read them fairy stories and come to my computer and start advising people how to get an assisted death.

"It's not exactly a life I would have chosen, but it's how life is."

Record number of submissions

A parliamentary inquiry into euthanasia has drawn more than 19,000 submissions, believed to be the largest number with "unique content" ever made on any political issue in New Zealand.

Health select committee staff are still processing the submissions. Only 2337 have been uploaded so far on to the parliamentary website.

The total is expected to fall short of the 21,533 submissions received on Louisa Wall's same-sex marriage bill in 2013, but most of those were standardised postcards and only 2898 contained "unique content".

This time health committee chairman Simon O'Connor said most submissions were unique.

I persuaded him to have palliative care. He is alive today, 25 years later.

Submissions closed on February 1. The select committee is expected to start hearing oral submissions in the next month.

It would probably travel around the country and aimed to complete the inquiry this year.

Matthew Jansen of the Care Alliance, which opposes euthanasia, said most submissions were based on personal family experiences.

Submissions have come from around the world, including one from South Africa-based Kiwi scientist Dr Sean Davison, who has told MPs that his mother was "hugely relieved" when he agreed to her request to give her a lethal dose of morphine to speed her painful death from cancer in 2006.

British palliative care specialist Baroness Ilora Finlay argues against euthanasia because doctors often don't know when someone will die.

She cites a man who asked her to help him die when doctors gave him less than three months to live in 1991.

"I persuaded him to have palliative care.

"He is alive today, 25 years later, and living well despite some disability imposed by his tumour," she says.